This invention relates to an air-flow metering device for a fuel injection system of an internal combustion engine, which meters the amount of the air flowing into the engine to precisely determine the corresponding amount of the fuel, thereby to supply optimum air-fuel mixture into the engine.
In a conventional air-flow metering device, a flap or a wind wheel is installed in the intake pipe, in which the inclination of the flap or the revolution of the wheel is taken as the representation of the air flowing into the engine, thereby to determine the amount of the fuel to be injected. However these conventional devices have some drawbacks, which are explained as follows. In case of installing the flap, as the flap is responsive to the vacuum pressure difference produced between the upstream and the down stream of the flap, when the throttle valve is opened widely, it is affected by the fluctuation of suction pressure of the engine. Further a check valve is required to protect the flap from engine back fire. Furthermore since the inclination is not proportioned to the amount of the air flow, a potentiometer is requried to provide complex characteristics to get a precisely correct signal with resultant high cost. On the other hand, in the case of an installed the wind wheel, it may be rotated excessively by its own inertia thereby to result in bad response, when the air velocity goes down rapidly. Further, as it produces an AC signal, it necessitates a D-A converter to get an analog signal representing the air flow, resulting in high cost.